I am working on another custom exhaust and I have the following measurements. The header terminates in a male tube 1.66-1.69" OD depending on where you measure it. I found 1.75" SS exhaust tubing 16g would be 1.75-(0.065*2) or 1.62" ID 1.75" 18g (0.049" wall) would be 1.652" theoretically. http://www.mandrel-bends.com/catalo...18-gauge-304-stainless-straight-tube-390.html I know I am going to need to massage this tubing slightly to make that joint a nice slip fit. I've read some reviews of exhaust pipe expanders on Amazon etc and did not get a good feeling but I am only trying to get a little bit of diameter out of this tubing. http://www.amazon.com/Lisle-32500-Exhaust-Pipe-Expander/dp/B0002STSNU Suggestions including buying new tools or having a shop do it?